1. Field of the Invention
The present invention relates to an endoscope in which an image pickup device capable of reading out a pixel signal from any selected pixel among a plurality of pixels such as a MOS image sensor or a CMOS image sensor is used in an image pickup unit.
2. Description of the Related Art
In order to observe a place where observation is difficult such as an inside of a body of an organism or an inside of a structure, an endoscope including an image pickup unit for picking up an optical image in a distal end portion of an insertion section insertable from an outside into the inside of the organism or the structure is used in, for example, a medical field and an industrial field.
For example, as disclosed in Japanese Patent Application Laid-Open Publication No. H10-146312, an image pickup unit of an endoscope includes an objective lens that forms an object image and an image pickup device disposed on an image forming surface of the objective lens. A CCD (charge coupled device) is often used as the image pickup device of the image pickup unit of the endoscope.
In an endoscope including, in an insertion section, a treatment instrument channel for projecting treatment instruments such as a needle and a forceps from a distal end portion, outer diameters of the treatment instrument channel and the image pickup unit are relatively large among a plurality of components disposed at the distal end portion. Therefore, an outer diameter of the distal end portion of the insertion section of the endoscope including the treatment instrument channel is mainly set according to the outer diameters of the treatment instrument channel and the image pickup unit.
In general, in an image sensor capable of reading out a pixel signal from any selected pixel among a plurality of pixels such as a MOS image sensor or a CMOS (complementary metal oxide semiconductor) image sensor functioning as an image pickup device, compared with a CCD, a peripheral circuit formed around a pixel formation region is large.